Electric servomotors are used extensively in numerically controlled (NC) machines, robots, and other industrial equipment. Any given industrial process consists of a repetitious sequence of steps such as advancing or rotating a tool or other load mechanism. To automate the process with an NC machine or the like, a servomotor is connected to drive the tool or load mechanism and the individual process steps are characterized in terms of the motor operation (velocity or position) required to perform the steps. A computer or machine code corresponding to the required motor operation is determined and stored in a step sequencer which is effective to repetitively issue a series of servomotor commands in the correct sequence. A motor controller is responsive to the commands issued by the step sequencer and is operative to energize the servomotor with current from an electrical source in a manner to bring the particular motor operating parameter (velocity or position) into correspondence with the command for performing the process step. Typically, the level of motor energization is determined as a function of a gain factor and the difference or error between the actual and command values of the specified motor operating parameter. At the time of installation, the motor controller gain factor is manually adjusted to achieve stable motor operation throughout the course of the process. If the gain factor is too high, the motor oscillates or rings about the commanded parameter value; if the gain factor is too low, the commanded parameter values are attained too slowly, if at all. The process steps are only correctly performed if the gain factor is properly adjusted.
A problem with servomotor driven process controllers of the above type is that the coulomb friction of the servomotor changes over time. When the servomotor is new, the bearings which support the motor rotor are relatively tight resulting in a fairly high level of coulomb friction. As the machine wears in, the coulomb friction decreases and then subsequently increases with wear. The level of coulomb friction also changes whenever the motor bearings are lubricated. In addition to the load torque T.sub.L, the servomotor must overcome its own coulomb friction torque T.sub.C to drive the load mechanism through the commanded sequence of process movements. If the motor controller gain factor is properly adjusted when the servomotor is new, it subsequently becomes necessary to readjust the gain factor for changes in the motor coulomb friction to maintain the desired level of motor stability. For example, the gain factor must be periodically reduced as the motor wears in, and subsequently increased with motor wear. The changes in motor coulomb friction occasioned by motor lubrication must also be compensated for by manual adjustment.